416 THE CHEMISTEY OF ESSENTIAL OILS
ing towards the engine is embedded in such a manner that steam fronp
the boiler may be admitted at will, either into the double walls of the
cylinder or into the interior of the cylinder itself; while the hollow pas-
sage in the other axle communicates with a condensing worm, the outlet
of which descends into a cylindrical vessel, 3, intended to receive the
condensed products, consisting of water and essential oil. When the
apparatus is first set in motion, the pump begins to produce a vacuum
during the first revolutions of the cylinder. Steam being now cautiously
admitted into the double walls of the cylinder, the water is raised to boil-
ing at a comparatively low temperature, and the vapours charged with
the essential oil rapidly pass over into the receptacle. With a two-horse-
power engine and a boiler designed for a five-horse-power engine, five
such machines may be driven at once, and the operation, including the
time required for charging and emptying, is completed in three-quarters
of an hour.
The United States Department of Agriculture have recently devised a
machine for the peeling of citrus fruits and the expression therefrom of
the essential oil. Although only in the experimental stage, it promises
to be very successful.
Lemon oil vari- s to a considerable extent, according to the period of
the harvest, to the season, and to the climatic conditions, so that it can
only be properly judged by the analyst when all these features are taken
into account.
The greater part of the oil of commerce is produced in the district of
Messina, on the north-east of the island of Sicily, and the adjacent dis-
tricts along the coast to the west; a considerable amount is produced in
the Palermo province, and all along the east coast of the island; and a
large amount also in Calabria, which is chiefly exported from Eeggio.
An approximate idea of the relative production of these districts is seen
from the export returns during 1905, which were as follows :—
From Messina 742,567 kilos.
„ Reggio 95,319 „
„ Palermo 26,041 „
„ Catania 4,317 „
| Apart from the alteration in rotatory power suggested above as coin-
ciding with the time of the crop, although possibly having no direct rela-
tion to the quality of the oil, it is found that the oil obtained from round
about Barcelona (near the northern coast) and from the plains of Syracuse
(on the south-eastern coast) possess the highest average rotations of all
the oils, this figure varying from + 64° to + 65°. The following figures
are found for the various districts :—
From + 57° to + 71°.. Messina and neighbourhood, Nizza di Sicilia.
„ + 61° „ + 63°.. Acireale, S. Teresa di Riva, Scaletta, S. Lucia.
Patti, S. Agata, S. Stefano.
„ + 63° „ + 64°.. Catania, Giarre, Giardini, Acireale, Lentini.
i „ + 64° „ + 65°.. Barcelona, Syracuse.
- • • Palermo oils are usually about + 57° to + 61°, and the Calabrian
oils + 59° to + 62° 30'. In the author's experience these limits are of
very small value and cannot be taken as in the least degree conclusive.
Cool rainy weather appears to have some effect on the optical rotation,
but all one can say conclusively is that the average rotation observed
during one season's crop is sometimes 2° or 3° higher or lower than that
of the preceding year. The Palermo oil and the Messina oil differ some-
